Some currently available implantable medical leads, such as Medtronic, Inc.'s model 3830 leads, have electrodes that are coated with drugs, such as beclomethasone dipropionate (BDP). In some cases the drugs are coated; e.g. dipped or sprayed, directly on the electrodes after the leads have been built. Without polymer binder, the coating process can be challenging. For example, coating uniformity can be difficult to achieve. In addition, testing of the coating in these cases can be costly because testing must occur on an entire lead. Accordingly, if coating of the electrode does not meet manufacturing specifications, the entire lead is scrapped.
It would be desirable to coat the electrodes earlier in the manufacturing process so that the coating of the electrodes may be tested before incorporation into the leads. This would significantly reduce scrap costs because the electrode, as opposed to the entire lead, could be rejected if the coating did not meet specifications. However, because coatings of drugs applied directly to electrodes are not typically very durable, such direct coating is often not possible earlier in the manufacturing process.
One way to improve the durability and coating consistency of the drug is to incorporate the drug into a polymer matrix. However, many polymers are electrically insulating and thus would be functionally incompatible for coating of an electrode. Further, the biocompatibility of many electrically conductive polymers is not yet known. Selection of a polymer for coating of an electrode that is biocompatible and that does not significantly interfere with the electrical properties of the electrodes can be challenging.
One category of polymers that have been shown to be biocompatible and to have good drug elution properties are the polymer blends described in U.S. Pat. No. 8,088,404. The polymer blends described in U.S. Pat. No. 8,088,404 includes blends of a homopolymer, a copolymer and a terpolymer. The terpolymer comprises monomer subunits of vinyl acetate, alkyl methacrylate, and N-vinylpyrrolidone. The copolymer comprises monomer subunits of vinyl acetate and alkyl methacrylate. The homopolyer comprises polyvinyl pyrrolidinone. U.S. Pat. No. 8,088,404 discloses that such polymers, with an associated drug, may be used to coat implantable medical devices such as pacemaker leads. However, U.S. Pat. No. 8,088,404 does not disclose whether such polymers have suitable electrical properties for coating electrodes of such leads, and the chemical nature of suggests that they may be electrically insulating.